Brian Meara, 63, is the person referred to in court papers as “the Lobbyist” who revealed that Silver told him “there was nothing to worry about” regarding the speaker secretly sharing in legal fees paid by Meara’s client, billionaire developer Leonard Litwin, the sources said.

Manhattan US Attorney Preet Bharara has said those payments to Silver — from a law firm run by Silver’s former Assembly counsel — were one way he “illegally monetized his public position” through a corruption scam that dates back to at least 2000.

Meara, 63, has been friends with Silver for decades and is among the state’s most powerful lobbyists, with offices in both Manhattan and Albany.

His relationship with Silver dates back to the 1970s, when they met in the Manhattan courthouse where Silver worked as a law clerk for Civil Court Judge Francis Pecora and Meara was a young court officer.

“The fact that Meara is the witness is not a good sign for Shelly,” said one Albany insider, alluding to how much Meara knows about his pal.

In addition to the state court officers union and other labor groups, Meara represents a host of big-bucks industries, including casino operators, insurance companies and soft-drink makers.

New York Assembly Speaker Sheldon Silver, center, is driven by federal agents to federal court on Jan. 22.AP

His clients also include the Yankees owners and the Silvercup Studios production facility in Queens.

The Bayside resident is also close to Queens Democratic boss and US Rep. Joe Crowley, while his brother, Chuck, was chief of staff to former City Council Speaker Christine Quinn.

A nephew, Assemblyman Ed Braunstein (D-Bayside), also formerly worked as one of Silver’s legislative aides.

According to Thursday’s criminal complaint against Silver, Meara got a non-prosecution deal from the feds in exchange for agreeing to serve as a “fact witness” against the Manhattan Democrat.

The complaint says Silver got two developers — including “Developer-1,” identified by sources as 100-year-old Litwin — to hire the law firm run by Silver’s former counsel, identified by sources as Jay Arthur Goldberg.

Silver allegedly pocketed at least $700,000 by splitting the fees generated by the lucrative property-tax challenges, without notifying either developer or disclosing the payments.

When the other partner at Goldberg’s firm, identified by sources as Dara Iryami, got worried that new legislative rules would require Silver to disclose the payments, the firm drafted new retainer agreements outlining the fee-sharing arrangement with Silver, the complaint says.

But in December 2011, shortly before the new retainer agreements were sent out, Silver phoned Meara, the complaint states.

Silver allegedly asked Meara if his lobbying of Silver on real estate issues was based on his representation of Litwin or the limited-liability companies, or LLCs, “that nominally owned the buildings ultimately owned by” Litwin.